Re: Partition-wise join for join between (declaratively) partitioned tables

Here's set of patches rebased on the latest head.

This rebase mainly changes patch 0001, which translates partition
hierarchy into inheritance hierarchy creating AppendRelInfos and
RelOptInfos for partitioned partitions. Because of that, it's not
necessary to record the partitioned partitions in a
PartitionedChildRelInfos::child_rels. The only RTI that goes in there
is the RTI of child RTE which is same as the parent RTE except inh
flag. I tried removing that with a series of changes but it seems that
following code in ExecInitModifyTable() requires it.
1897 /* The root table RT index is at the head of the
partitioned_rels list */
1898 if (node->partitioned_rels)
1899 {
1900 Index root_rti;
1901 Oid root_oid;
1902
1903 root_rti = linitial_int(node->partitioned_rels);
1904 root_oid = getrelid(root_rti, estate->es_range_table);
1905 rel = heap_open(root_oid, NoLock); /* locked by InitPlan */
1906 }
1907 else
1908 rel = mtstate->resultRelInfo->ri_RelationDesc;

I don't know whether we could change this code not to use
PartitionedChildRelInfos::child_rels. Removing
PartitionedChildRelInfos machinary seems like a separate patch.

The last two patches implement the advanced partition matching
algorithm and are here in this set for ready reference. Please use [1]
for discussing/reviewing those.

[1] https://www.postgresql.org/message-id/CAFjFpRdjQvaUEV5DJX3TW6pU5eq54NCkadtxHX2JiJG_GvbrCA@mail.gmail.com
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Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company